1. Field of the Invention
The present invention relates to a flowmeter and, more particularly, to a flowmeter to be assembled in a fluid therapy line for continuously injecting a therapeutic fluid into the body of a patient at a very low rate in order to prevent formation of a thrombus in a catheter when the catheter is indwelled in the patient's body over a relatively long period of time in an invasive blood pressure monitoring system or the like.
2. Description of the Prior Art
Conventionally, a fluid therapy line has an intravenous drip chamber for measuring the flow rate of a therapeutic fluid injected into a patient's body. Such an intravenous drip chamber is also used in an invasive blood pressure monitoring system. However, flow rate measurement with an intravenous drip chamber requires a relatively long period of time and may cause introduction of air into the patient's body during flushing or the like.
As a fluid therapy flowmeter free from this problem, a flowmeter using a float is described in U.S. Pat. No. 3,034,504 or Japanese Patent Publication No. 50-31466. However, when this type of flowmeter is assembled in an invasive blood pressure monitoring system connected to a flushing device, the float is caused to abut against the wall of the fluid outlet port by the excess fluid flowing during flushing. Even after the flow rate recovers to the normal value, the float remains attached to the wall and does not return to the original position. Then, a prescribed micro flow rate cannot be obtained, resulting in an unsatisfactory result.